1. Field of the Invention.
This invention relates to calenders, and more particularly to calender roll positioning.
2. Prior Art.
Calenders are used in the rubber and plastic industry to form or process sheet or web stock. Web or sheet thickness is controlled by the spacing between two opposed calender rolls, one of which is adjustably mounted so that the spacing can be varied. Roll positioning means that will accurately locate the rolls and adjust the roll pressure to maintain a spacing are desired to obtain uniform thickness of the stock. The product in some arrangements is sensed downstream from the calender rolls and adjustments made in the roll spacing to compensate for factors such as machine distortion that affect product thickness. A measurement or condition change indicative of the positional relationship between the rolls may be used to initiate and control an adjustment in the roll spacing.
Certain arrangements for adjusting one roll of a calender or mill for control of workpiece thickness are already known, but in one way or another, do not satisfy all presently desired objectives. Typical systems utilize power screws, fluid actuators, or combinations where a screw and fluid actuator act in series to position a movable roll. Spacing is controlled in many instances from machine and/or workpiece sensors, such as position-sensitive transducers and thickness gauges, and product thickness has also been controlled by the speed of a calender pick off. Feedback loops are used to facilitate continued adjustment of roll spacing or other operating parameters to enhance control over product thickness. Some examples of known systems of the above type are shown in U.S. Pat. Nos. 3,479,951; 3,531,827; and 3,600,747.